This invention relates to preoperative evaluation techniques and more particularly to a method and apparatus for analyzing the rotational and translational movements in the horizontal plane that are required to correct an anomaly of facial bilateral symmetry.
The majority of orthognathic cases that come to surgery involve deformities predominantly in the sagittal plane. Some of these may also have minor midline discrepancies (with or without a crossbite) based on irregularities in the symmetry of one or both dental arches at the dentoalveolar level. However, cases in which the dominant feature is an anomaly of bilateral symmetry in one or both jaws at the skeletal level are relatively rare.
Cases with major or minor discrepancies in the horizontal plane as an isolated phenomenon, or in association with one of the more usual sagittal discrepancies tend to be the most challenging to evaluate preoperatively, even though they may ultimately be treated in a routine surgical manner.
Various types of work-up techniques are available to the surgeon for different kinds of deformities. Certain techniques are better than others in terms of the corrective movements that they best measure. The lateral cephalometric X-ray averages facial anatomy in the mid-sagittal plane and thus documents with great clarity the vertical and anteroposterior aspects of facial anatomy. However, because this technique averages the two sides it is practically useless in evaluating symmetry. Dental models, although confined to dentoalveolar structures, nonetheless accurately document the anatomy they record in all three dimensions. Such models are particularly usefull in revealing anomalies of bilateral symmetry. They can also be used to document both vertical and anteroposterior corrective movements in specific sagittal planes and to show vertical and lateral movements in a frontal plane.
What is lacking at the present time is a simple, effective method and apparatus for analyzing corrective movements in the horizontal plane. Unfortunately, this is exactly the plane in which one would want to measure disturbances in facial bilateral symmetry.
It is accordingly a general object of the present invention to provide a method and apparatus for analyzing the required rotational and translational movements in the horizontal plane.
It is a specific object of the invention to provide a method and apparatus for generating a graphical representation of jaw movements in the horizontal plane.
It is another object of the invention to provide a method and apparatus that utilizes the three dimensional information contained in a dental model.
It is still another object of the invention to provide an apparatus that produces an accurate and reproducable positioning of an articulated mandibular model at two unique positions.
It is a feature of the invention that the positioning of the articulated mandibular model is accomplished without reference to scalar measurements.
It is another feature of the invention that the method thereof can be implemented with relatively simple and inexpensive hardware without sacrificing the requisite degree of measurement accuracy.